The present invention relates generally to amplifier arrangements and in particular to a low-voltage, complementary symmetry amplifier circuit particularly adapted for integrated circuit implementation and especially suited for audio processing applications.
There is, of course, a need for amplifier devices that are capable of handling significant current levels. Output amplifiers are but one example. In hand-held, personal communications apparatus, and in radio pocket pagers, in particular, such amplifiers may drive a loudspeaker or, in the case of a tone-only device, perhaps a transducer device of some sort.
In subminiature devices of this character, space requirements are, indeed, critical. However, of equal criticality, is power efficiency, since such apparatus must function from a self-contained battery source. Accordingly, this customarily dictates more than one output transistor device so as to permit class B operation, with its attendant current consumption efficiency in the output devices, under no signal input conditions. For stacked transistors of the same type, it is difficult to operate at low supply voltages, particularly below about 1.4 volts DC. Furthermore, a transformer is usually required which, in low-voltage supply applications, has a severely limited swing that the output transistors may effect. The transformer also consumes valuable space, adds weight, and reduces circuit efficiency due to its inherent internal losses.
Accordingly, a need exists for an amplifier arrangement which operates at low supply voltage, on the order of one volt, and which nevertheless avoids the high stand-by currents of prior devices. The amplifier should, except for the output transistor devices themselves, be easily implemented in integrated circuit form.
It is an object of the present invention to provide an improved low-voltage, complementary symmetry, class B audio amplifier arrangement operating efficiently on supply voltages of less than 1.4 volts DC.
It is another object of the present invention to provide an improved amplifier of the foregoing type which does not require a transformer as an integral component so as to allow circuit fabrication in a minimum of volume and cost.
Yet another object of the present invention is to provide an improved amplifier of the foregoing type which avoids low level output voltages.